The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer.
In manufacturing high-integration circuit devices and optical devices, elements of these devices, such as semiconductor wafers and optical lenses, are required to be polished to a high degree of uniformity. In recent years, in order to meet this requirement, a so-called CMP (chemical mechanical polisher) has been commonly used as a polishing apparatus for polishing semiconductor wafers. In a CMP, a semiconductor wafer is held by a wafer holder or carrier, which proceeds to lower and press the wafer against a polishing surface comprising a flexible polishing pad of a rotating turntable. The wafer is then subjected to a relative sliding motion relative to the polishing surface of the turntable while, at the same time, an alkali abrasive liquid is supplied to the polishing surface. By using this combination of mechanical and chemical polishing, highly precise polishing of a wafer can be achieved. Since in a polishing operation using a CMP, friction is generated between a wafer and a polishing surface, lateral displacement of the wafer may occur. To avoid displacement of the wafer, a retainer ring is generally employed. In FIG. 5, a retainer ring 1a is shown which is formed on a carrier 1 around its outer circumferential edge. In addition to a danger of lateral displacement of a wafer during polishing, there is also a danger that its circumferential edge may be overpolished if the edge is subjected to excessive pressure when the sliding motion is effected while the wafer is pressed against a polishing surface (reference is made, for example, to Unexamined Japanese Patent Application Public Disclosure No. 10-58309). Thus, as shown in FIG. 5, conventionally, a pressure ring 3 is provided outside and separate from the retainer ring la on the carrier 1. During polishing, the pressure ring 3 depresses the flexible polishing pad comprising the polishing surface around the semiconductor wafer 4 by an amount sufficient to prevent the circumferential edge of the wafer to be polished from being subjected to excessive pressure and polishing during a relative sliding motion between the wafer and the polishing surface. Preferably, the pressure ring is positioned as close as possible to the circumferential edge of the wafer held on the carrier.
However, in the conventional polishing apparatus in which a retainer ring is positioned between a pressure ring and a wafer, a distance of around 2 mm exists between the pressure ring and the semiconductor wafer and it has been desired to reduce this distance.
It is an object of the present invention to provide a polishing apparatus which enables a reduction in the distance between a circumferential edge of a wafer held on a carrier and a pressure ring.
In accordance with the present invention, there is provided a polishing apparatus comprising a carrier having a pressing surface to be engaged with a platy workpiece such as a semiconductor wafer to press the workpiece against a polishing surface, whereby the workpiece is polished by being subjected to a relative sliding motion relative to the polishing surface while being pressed thereagainst, the pressing surface including a suction opening for applying a vacuum to hold the workpiece on the pressing surface during polishing of the workpiece.
The pressing surface may include a recessed portion formed at a desired position, which recessed portion has the suction opening and is communicated with a negative-pressure gas source or vacuum source provided outside the carrier, so that a vacuum can be applied to the recessed portion by the vacuum source and the platy workpiece can be securely held on the carrier under the effect of the vacuum. Preferably, the recessed portion extends along an outer peripheral portion of the pressing surface. More preferably, the recessed portion is arranged in the form of an annular groove.
Specifically, the carrier comprises a carrier body having a generally disk-like configuration and a backing plate covering the surface of the carrier body facing toward the polishing surface. The surface of the backing plate facing toward the polishing surface provides the pressing surface. This surface of the backing plate includes the recessed portion arranged in the form of an annular groove and a pressure-applying recessed portion formed radially inward of the groove. The pressure-applying recessed portion is communicated with a positive-pressure gas source or fluid pressure source provided outside the carrier. The backing plate may be made of gas-impermeable resilient material.
The present invention also provides a polishing apparatus comprising a carrier having a pressing surface for pressing a platy workpiece such as a semiconductor wafer against a polishing surface, and a pressure ring to be positioned outside and adjacent to the workpiece held by the carrier for pressing the polishing surface around the workpiece. The workpiece is polished by being subjected to a relative sliding motion relative to the polishing surface while being pressed thereagainst. The pressure ring and the carrier are capable of rotating relative to one another. Since the pressure ring is provided adjacent to the workpiece, the polishing surface can be depressed to an optimum level relative to the workpiece. Further, since the pressure ring and the carrier are capable of rotating relative to one another, it is possible to avoid a situation that when a lower surface of the pressure ring is undulating, a specific portion of the workpiece is affected by such undulation. This ensures high overall uniformity in the polishing of the workpiece.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.